Recently, many vehicles are provided with an automatic air conditioning system which automatically controls an air conditioner of vehicles.
FIG. 1 shows a construction of such an automatic air conditioning system. In the system, the air conditioning operation is so effected that air sucked by a fan 10 is cooled by an evaporator 1 and then a heater 2 through which hot water flows heats air which is blown out into a compartment of a vehicle by fan. The temperature of the blow out air is controlled by an opening of an air mix damper 3. The damper is controlled by a control unit 4 on the basis of a setting value of a temperature, a temperature in the compartment, a temperature of a duct and the quantity of solar radiation. The setting value of the temperature is set by a temperature setting resistance 5. The temperature in the compartment is sensed by a temperature sensor 6. The quantity of solar radiation is detected by a solar radiation sensor 7.
FIGS. 2(A) to 2(D) show a voltage for driving the fan, an opening of the air mix damper, a temperature of the blow out air into the compartment and a state of a hot water valve for the heater with regard to a load in the cooling and heating mode in a conventional automatic air conditioning system, respectively.
In a curve of the temperature of the blow out air into the compartment shown in FIG. 2(C), a line a shows a temperature of air sent out of the evaporator 1. An arrow b shows a reheated temperature (a difference between the temperature of the blow out air into the compartment and the temperature of the air sent out of the evaporator 1). An arrow c shows a region in which a compressor 9 for cooling is not used (in the case of the heating operation), and an arrow d shows a region in which an energy loss is produced (a reheating region after cooling).
As apparent from FIG. 2(C), the air conditioning operation of the conventional automatic air conditioning system is made by maintaining the blow out air temperature from the evaporator 1 constant in the cooling operation and then adjusting the air mix damper 3 (i.e. by adjusting the mixture ratio of cool air and hot air passing through the heater 2). Thus, in view of saving energy, which has become important due to the high price of gasoline, the conventional automatic air conditioning system in which air cooled by the evaporator 1 is reheated by the heater 2 to perform the air conditioning operation is operated to oppose the energy savings.
Further, a controller for the conventional automatic air conditioning system has been so constructed that a fan change-over switch 8 and a damper actuator for controlling the cooling and heating operation are directly connected to each other. Therefore, since the compressor 9 must be always operated even in spring or autumn that the cooling load is less, it is difficult to effectively attain an energy saving operation.
Furthermore, even if a vehicle is provided with the above automatic air conditioning system, a cooling operation is niot often made in a cold area, for example, a north district. However, a manual operation of controlling the opening of the air mix damper and a fan driving voltage lacks commercial attraction. Accordingly, a controller for automatically controlling a temperature only in the heating mode has been desirable.